In conventional gravity separators, differences in the specific gravities of the different individual minerals or phases making up the mixture known as the feed material are used to accomplish the separation. Generally, a stream of the feed material flows over a downward sloping surface under the influence of the force of gravity. Typically, the surface is an inclined plane or cone, or spiral. The higher specific gravity particles, which generally become the concentrate (e.g. wolframite, magnetite, tin, gold), tend to settle near the bottom of the stream of feed material, while the lower specific gravity particles, which generally become the tailings, tend to congregate near the top of the stream. Alternatively, in particular applications, it is the particles which congregate near the top of the stream which are saved while the particles which settle near the bottom are discarded. Various means, some of which are described below, are used to divide the top of the stream from the bottom of the stream so as to separate the tailing and concentrate.
In practice, many minerals such as wolframite, a source of tungsten, are magnetic or weakly magnetic and have a high specific gravity. Wolframite is usually separated from its ore in two distinct stages, the first stage being gravity separation and the second stage being magnetic separation. More particularly, the first stage typically involves wet gravity separation of ground wolframite ore using one of the conventional gravity separators e.g. cones, spirals, shaking tables, pinched sluices, etc. The wet gravity concentrate is then dried and subjected to dry magnetic separation to produce a tungsten concentrate. Such dry magnetic separation may be accomplished with the magnetic and gravity forces working against or opposite one another.
The performance of a conventional gravity separator in separating high specific gravity magnetic or weakly magnetic minerals from their ores can be improved by combining the gravity force with codirectionally acting magnetic forces. The reason for this is that the resultant of the gravity and magnetic forces is more effective in causing high specific gravity magnetic or weakly magnetic particles to settle at the bottom of a stream of feed material than is the gravity force acting alone. One resulting advantage is the recovery of relatively fine-sized magnetic or weakly magnetic particles which are often difficult to recover using a conventional gravity separator. While not eliminating the need for the separate magnetic separation stage in the above described process for recovering wolframite, adding magnetic forces to a conventional gravity separator improves both the capacity of the gravity separator and the grade of concentrate produced by the gravity separator.
An ore separator in which substantially codirectional magnetic and gravitational forces are used to concentrate magnetic or weakly magnetic minerals is disclosed in Martinez, "The Concentration of Weakly Magnetic Minerals", The Pennsylvania State College Department of Mineral Engineering, Masters Thesis, 1953, a lone copy of which was deposited in the library of Pennsylvania State College. In this separator, a plurality of stationary permanent magnets is located beneath and along the length of an inclined planar surface which is formed by the uphill moving portion of a continuously moving endless belt. Wet ore is fed onto the belt and tends to move downhill. However, the magnetic or weakly magnetic particles in the ore are attracted by the magnets located beneath the moving belt and are moved uphill by the moving belt. In this ore separator, the tailing is collected at the bottom of the incline and the concentrate is collected near the top of the incline. The belt is used so as to continuously move the magnetic or weakly magnetic particles away from the magnets to which they are attracted. If this is not done, the magnetic or weakly magnetic particles will build up on the separator surface at sites corresponding to the locations of the magnets and wi11 in time upset the concentration process by selectively blocking flow of the wet ore, thereby creating undesirable eddy currents. In addition, the build up of magnetic or weakly magnetic particles on the separator surface may ultimately distort or shield the magnetic field. In addition to including the desired magnetic or weakly magnetic particles, the unwanted build up may also include other types of magnetic or weakly magnetic particles.
The processing of most ores containing desirable magnetic or weakly magnetic minerals requires crushing and grinding of the feed material to a fine size. Crushing and grinding introduces into the ore mill iron, abraded from the crusher, grinding mill liners, rods, and balls. This material is highly magnetic. In addition, many ores containing desirable magnetic or weakly magnetic minerals also contain magnetic or weakly magnetic minerals, such as pyrrhotite (FeS), which may be considered gangue or worthless material. The mill iron, as well as the worthless magnetic and weakly magnetic minerals will be attracted by the magnetic field and will, if a means is not used to allow them to be removed from the separator surface, build up near the magnets. An alternative solution to the problem of build up of magnetic particles is disclosed in Japanese Pat. No. 143967. The Japanese patent discloses a separator in which a slurry of coal and iron ore flows along the bottom of a separation tank while the slurry is agitated by water coming from sprinklers. The iron ore sticks to the bottom of the tank which is magnetized by electromagnetic coils while the non-magnetic materials are washed away. Scrapers are used to remove the built up iron ore from the tank bottom.
While the above described gravity-magnetic ore separators may, under certain circumstances, exhibit improved concentration capability for magnetic or weakly magnetic minerals, no means has heretofore been disclosed for providing conventional gravity separators such as Wright concentrators, cones, pinched sluices, spirals, shaking tables, etc. with magnetic forces so as to improve the ore concentrating capabilities of such standard gravity separators. One reason for this is that no adequate solution to the problem of preventing build up of magnetic materials on the flow surface of a conventional gravity separator equipped with magnetic force applying means has heretofore been proposed. Accordingly, it is an object of the present invention to provide means for modifying conventional already existing gravity separators with magnetic force applying means so as to improve their ore concentrating capabilities while at the same time inhibiting the build of magnetic materials.